I gave a talk in the 2011 JVM Language Summit, at Oracle, Santa
Clara. The talk is now online and you can watch the talk at this
link. I've also embedded the talk below. You can download the PDF of
the slides here.

ASM is a java byte-code generator and modifier tool. It is under
active development and it's developers are moving towards releasing
version 4 of the library. During the process they have changed most
interfaces in the library to abstract classes. See the complete
change-log at this link.